Latest from Cassini
By Molly Michelson
At the recent AAAS meeting in Boston, I met Amanda Hendrix from NASA’s Cassini Mission. Dr. Hendrix, a planetary scientist, has been with Cassini since 1999, when Cassini flew by Earth’s Moon. “I became involved with the UVIS (the Ultraviolet Imaging Spectrograph) team to analyze the Moon data. The next year, I began working with the Cassini Project team at JPL as part of the Science Planning team, to plan out the science investigations that would happen during each icy satellite flyby.” Now she uses data from UVIS to study the icy moons of Saturn.
Cassini has returned so many stunning results over the last nine years, I thought I’d get the latest from her. Here’s an excerpt of our email interview.
Where is Cassini right now? What is it studying?
Cassini is in a highly inclined portion of its tour of the system, so that its path is ~60° out of the plane of Saturn’s equator. This provides Cassini’s instruments access to wonderful views of the polar regions of Saturn and Titan, and also a unique perspective on the rings system.
After spending the last couple of years in the equatorial plane, it is great to get some beautiful views of the rings, and to understand how they are evolving on the timescales of a few years. High latitude views of the planet and Titan mean that we can observe critical seasonal variations happening in the Saturn atmosphere (such as the development of the giant “serpent” storm) and the Titan atmosphere (such as the formation of the southern hemisphere polar hood) and on the Titan surface (we can watch for changes in the lakes and seas at the southern and northern polar regions).
Looking for and studying seasonal variations is important because it helps us to piece together the clues to understand solar system processes and will ultimately aid in the study of the formation and evolution of the solar system.
Can you highlight some of Cassini’s recent discoveries?
There are several studies being undertaken to understand the variability (if any) of Enceladus’ activity, and its ice grain and water vapor output, with orbital location. Some models have shown that the gravitational stresses vary, depending on where Enceladus is in its orbit, and this might affect the plume output. So those studies are ongoing and interesting.
On another topic, Cassini images have been used to show that Titan “glows” from deep in its atmosphere, as seen while Titan was in Saturn’s shadow. The likely cause is deeply-penetrating particles (such as cosmic rays) that excite the atmospheric gases. Another discovery is that there could be icebergs—of hydrocarbon ice—floating on the lakes of Titan. This comes from the radar images of the lakes along with calculations that if some amount of Titan atmosphere is contained within the methane ice, it will float rather than sink.
What’s next for Cassini?
Cassini will remain in the inclined phase of orbits until around February 2015 (it recently passed the peak in inclination and is now heading back down), then it will execute orbits roughly in the equatorial plane (for about a year), and this is when we will have two Dione and three Enceladus flybys. The final close flyby of the moon Rhea took place Saturday, March 9, 2013. We have numerous upcoming Titan flybys to study this intriguing moon and track its seasonal variations.
How much longer will Cassini be operational?
The plan is for Cassini to remain in operation, in orbit at Saturn, until September of 2017. An exciting end-of-mission is being planned, whereby Cassini orbits closer and closer to Saturn, with its orbital periapse (closest point to Saturn in the orbit) between the top of the atmosphere and the inner edge of the D-ring (the innermost ring), at high inclination. Such close passes will tremendously help the instruments on Cassini to measure the internal structure and magnetic field of Saturn, and will allow for a careful measurement of the mass of the rings—which is important in ultimately understanding their age and source! Finally, Saturn’s gravity will capture Cassini and the mission will be over.
What are some of your favorite findings?
The discovery of activity at Enceladus is one of my favorites! That such a small moon puts out so much material, with great effect on the rest of the system, is really astonishing and wonderful. This discovery was great because it was such a multi-instrument discovery and really highlights the utility of synergistic investigations on a mission.
Another one of my favorites is the discovery of liquid lakes on Titan—the only body in the solar system other than Earth with liquid on the surface! The landing of the Huygens probe on the surface of Titan was a really exciting time. Another of my favorite findings was the up-close views of bizarre Iapetus that we obtained during our close flybys with that moon.
Why do the data and images Cassini provides move people so much?
Cassini is such a great mission because the payload includes a complementary instrument suite that allows us to probe nearly every aspect of the Saturn system. The datasets are stunning and moving partly because the Saturn system is very beautiful. The intricate detail revealed in the images is wonderfully mind-boggling!
Recent Cassini image (with Venus hiding in Saturn’s rings): NASA/JPL-Caltech/Space Science Institute